Doctors now typically recommend at least SPF 30 – at least being the key words. "Just keep in mind: No sunscreen provides 100 percent protection. So to be safe as possible, you still need to reapply every two hours and after a swim, even if you used the water-resistant kind," said Joshua Zeichner, MD, Director of Cosmetic and Clinical Research in Dermatology at The Mount Sinai Medical Center. Learn more